Effect of metal exchange (Os vs. Ru) and co-ligand variation (Cl- vs. acac-) on the oxidation state distribution in complexes of an o-phenylenediamido(2-)/o-quinonediimine redox system

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Dalton Transactions, (2009)
DOI: 10.1039/b906913e


The compds. OsCl2L2 (1), RuCl2L2 (2) and Ru(acac)2L (3), L° = N-phenyl-o-quinonediimine and acac- = 2,4-pentanedionato, were synthesized and electrochem., spectroscopically and structurally characterized with the support of detailed DFT calcns. For the new Os compd. 1, the av. values for C:NH (1.331 \AA), C:NPh (1.345 \AA) and C:C (meta) bond lengths at 1.360 \AA agree more with an o-semiquinonediimine than with an o-quinonediimine formulation for the coordinated ligand, whereas the latter assignment is more appropriate to describe the Ru analog 2 (av. bond lengths of 1.308, 1.324, and 1.348 \AA, resp.). In turn, the corresponding av. bond lengths in 3 (1.333, 1.352, and 1.350 \AA, resp.) are suggestive of an o-semiquinonediimine ligand. DFT calcns. confirm the structural data and describe the electronic structures related to the oxidn. state assignments. The stabilization of trivalent Ru by electron donating acac- in 3 = RuIII(acac)2(L·-) and the preference of Os for higher oxidn. states (here: OsIVCl2(L·-)2 in 1) as compared to Ru analogs (here: RuIICl2(L°)2 in 2) in otherwise similar setting is responsible for these results. Oxidn. of the diamagnetic complexes proceeds to partly EPR and UV-visible spectroelectrochem. detectable cations with metal-centered spin, suggesting the following formulations: OsIIICl2(L°)2+ for 1+, RuIIICl2(L°)2+ for labile 2+, and RuIII(acac)2(L°)+ for 3+. In the case of 3, reversible metal-centered redn. results in ligand-based spin as compatible with a RuII(acac)2(L·-)- situation for 3-. on SciFinder(R)



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